1. Field of the Invention:
The invention relates to a method and apparatus for the transfer of rotary torque drilling energy from a power source to a drilling tip. More particularly the invention relates to method and apparatus of the character described for drilling a tight radius curved bore hole with a flexible rotary drill shaft.
2. Description of the Prior Art:
Many rotary drive apparatus exist for different particular purposes. Each flexible shaft rotary drive is designed to operate at acceptable levels for specific purposes and to accomplish operating parameters of certain specificity. None of the prior art referenced herein have been made to operate at requirements set by drilling a curved bore in a hard material. For example, most prior art reviewed and cited by applicant, although related to flexible rotary drill shafts and wire rope members, are cited for specific purposes unrelated to boring curved holes. These devices operate at very high RPMs and generally have different operating performance requirements. One such example is U.S. Pat. No. 4,686,982 to Nash which discloses a spiral wire bearing for rotating a wire drive catheter. This disclosure represents a typical type of flexible drive means which has no center core and is made to operate at very high speed, generally in excess of 20,000 RPMs. This basic design combination would fail in the drilling apparatus of the present invention due to the extreme loads encountered by the center of the present drilling energy transfer member (DETM).
Another type of prior art is a typical industrial flexible shaft configuration such as disclosed in U.S. Pat. No. 5,820,464 to Parlato which has a mandrel and six total layer wraps. These particular types of flexible shafts are made with multiple wraps of very small wires with the center comprising multiple wraps laid at a very steep helix pitch. The problem with this type of flexible shaft is that it is generally wrapped too tight and it is too stiff for the application of the present invention. Having been wrapped too tight and with a too stiff helical pitch at the center, it does not possess sufficient longitudinal strength or flexibility along the center to withstand high torque loads when passing around sharply curved radiuses.
Another such prior art example is disclosed in U.S. Pat. No. 4,185,473 to Troost. Troost discloses another example of too many lays or wraps, too many wires wrapped at too steep of a pitch angle. Also, another problem with the Troost shaft is that the pitch is too steep in the center wraps which are not laid for longitudinal linear strength along the center. This flexible shafting would also fail when put in the present operating environment since the strands are wrapped too tightly and the lack of flexibility would not allow for transmitting drilling energy around a tight curve radius. These types of flexible shafts generally have multiple wraps of wires that are substantially the same diameter and therefore are not balanced properly to handle the extreme loads experienced in multiple operating positions such as tight curves and straight operating runs.
The U.S. Pat. No. 5,052,404 to Hodgson discloses another type of torque transmitting device. This particular torque transmitter simply has too few coils and is therefor not flexible enough to withstand drilling around a tight radius. Another type of rotary transmitter is a rotary transmission conduit such as disclosed in U.S. Pat. No. 5,072,759 to Moore. The Moore transmission conduit includes an inner tubular liner comprised of polymer material and an outer layer of adhesive material. These types of devices usually comprise conduit made up of sub-assemblies of different types of wire wraps with additional component configurations. The problem with this type of devices is that the sub-assembly componentry takes up valuable space which reduces strength to below that required in a highly flexible curved drilling application. Yet another type of device is described in U.S. Pat. No. 5,165,421 to Fleischhacker et al. Fleischhaker et al discloses a lumen cable which is formed from helically wound inner and outer coils. The problem with this type of configuration is that no tensile or linear compression components exist within the structure and, as a result, failure will occur rapidly if linear stress is applied. All of these basic prior art designs would fail in the present tight radius curved bore drilling device because of the lack of balance, flexibility requirements and the extreme loads placed on the center of the DETM. Also there are balancing forces that are required in the DETM which must perform under multiple different positions during loading.
Wire rope is another type of prior art stranded configuration of some relevance. These configurations are manufactured primarily for linear travel over pulleys and are intentionally constructed so as not to rotate as they ride over a pulley. This approach teaches in the opposite direction from the present invention.
Finally my prior U.S. Pat. Nos. 5,700,265; 5,509,918; 5,002,546; and 4,941,466 represent prior art flexible shafting that has been used in a tight radius curved drilling. The problem with these rotary drives is that they do not balance the outer extensor and the inner compressor forces and hence have a reduced operating life. Their center configuration is not laid to withstand the necessary tensile loads and the outer torque layers are not wrapped for balancing the two outer lays with respect to each other and with respect to the center tensile compressor lays. Therefore, the operating life of this type of rotary drive is reduced.